In a typical known embodiment, a hydraulic cylinder is attached to the under surface of the table of a grinding machine, and by operation of a hydraulic cylinder, the table can be rapidly moved to and fro between a retracted position and an operating position and for this purpose there is provided a rotationally driven eccentric cam mechanism or assembly which acts on the end of a reciprocating shaft which extends into a cylinder. Thus the grinding wheel can be driven with a reciprocating movement.
Such an eccentric cam mechanism is conventionally composed of a slide-ring which is attached to the reciprocating shaft and an eccentric cam is disposed within the slide-ring so that it is slidably in contact with the ring to move it in a forward and backward direction, and a drive shaft rotates the eccentric cam and when the drive shaft is rotated, the eccentric cam undergoes an eccentric movement and by slidably contacting the inside of the slide-ring, the slide-ring is moved in a reciprocating manner in accordance with the degree of eccentricity of the eccentric cam. Furthermore, the eccentric cam is formed as two rings and the outer cam ring contacts the inner wall of the slide-ring and the traverse force component is restrained as much as possible and it can be made to slide only along the axial direction of the shaft to be reciprocated.
In the conventional cam mechanism, however, as the outer cam reciprocates, it strikes the inner wall of the slide-ring, the reciprocating movement is not a smooth sine-curve in accordance with the degree of eccentricity and, as shown in FIG. 1, a shock which is indicated by dotted-line occurs at the end point of its reciprocating movement. In order to eliminate this shock, the gap between the surface of contact of the outer and the surface of contact of the slide-ring, must be extremely small in size, but in this case, as the contacting surfaces meet during each reciprocating movement, there is excessive wear.